Blister packages consist of a lower web of a relatively thick material, which is configured such that cavities are created, and an upper web which is welded to the configured lower web, after a product has been filled into the cavities.
The lower web is frequently of PVC (polyvinyl chloride), but now and then also of APET (amorph polyester) or PP (polypropylene), and sometimes also with a layer of aluminium foil laminated to the polymer material—if the barrier requirements are very high.
Today, a relatively hard aluminium foil e.g. in 20μ is provided on most upper webs, through which the product (pill, chewing gum, etc.) may be pressed, but it cannot readily be approved as being childproof.
There are also types with pure aluminium which can be approved as a childproof blister package. Typically, these blister packages may be opened by making an area where the upper web forms a flap.
The childproofness is provided by using a somewhat tougher and optionally thicker aluminium foil which cannot be penetrated, or only with difficulty, it being instead necessary to peel or pull off the upper web. The childproofness is then that a preform of the lower web is made on a sheet, centrally between four cavities, where the upper web is not welded, and through which a perforation line extends. This means that a small snip is created which may be pulled when the upper web is to be peeled off the lower web in order to open a cavity.
Such a known blister package is described e.g. in German Utility Model DE 202004008975 U1 , which discloses a blister package with a lower web in which two rows of cavities are provided, and an upper web which is welded to the lower web. The blister package has perforation lines between adjoining cavities, which makes it possible to tear off one or more cavities from the blister package. The upper web and the lower web are not welded to each other in areas at the intersections of the perforation lines, thereby creating a snip which may be pulled in order to open the cavity.